With the increasing power demands of integrated circuit (IC) chips, there exists a need for IC chip packages to be designed for greater power delivery. Economics dictate that the cost of such packages be as low as possible while still delivering the necessary power to the IC chip and maintaining input/output (I/O) signal quality.
Conventional IC package substrates are made with a solid non-conducting core. FIG. 1 illustrates an example of just such a conventional IC package substrate. Core 102 is made up of a dielectric material, typically fiberglass. Since this material is nonconductive, it offers no electrical benefit for power delivery. Voltage rails (i.e., power and ground) and I/O signals are routed through plated holes, commonly referred to as “vias”, in the core. Metal layers 104 and 106 are disposed on either side of the core and can provide power or ground wells. Additional dielectric layers 108 and 110 insulate the metal layers from one another. In this case, as the power demands of the IC rise, it may be necessary to add more and more layers to the substrate in order to provide ample power and grounding to support such increased demands.
In contrast, FIG. 2 illustrates an example of an IC package substrate with a metal core 202 as taught by U.S. Pat. No. 5,847,327 issued Dec. 8, 1998 to Fischer et al. and entitled “DIMENSIONALLY STABLE CORE FOR USE IN HIGH DENSITY CHIP PACKAGES.” By coupling the metal core with a voltage rail, it is possible to leverage the electrical properties of the metal core and eliminate one or more of the metal layers that were needed as in FIG. 1. The core 202 is insulated with dielectric layers 204 and 206, which are typically made of an epoxy.
One of the limitations of the Fischer core 202 is that it is but a single continuous piece of metal. Accordingly, it is only possible to couple it to a single voltage rail. Other voltage rails may be coupled with additional metal layers 208 and 210.